Antenna



Nov.. 30, 1948. F50. CHESUS E+ AL 2,454,774

ANTENNA Filed Aug. 29, 1945 INVENTORS FMA/K 0. cHEsas Fan/vk G BY Patented Nov. 30, 1948 ANTENNA Frank O. Chesus, Jackson Heights, vand Frank G. Thomas, Islip, N. Y., assignors to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application August 29, 1945, Serial No. 613,329

(Cl. Z50-33) The present invention relates to short wave antennas, and, more particularly, to a new antenna design of the monopolar type, possessing certain desirable characteristics due to the novel design of the antenna.

It is a feature of our invention to provide a mechanically simple antenna of relatively small size and rugged construction, suitable for use on aircraft or vehicles, possessing in addition characteristics such as to enable employment of our invention in direction finding antenna arrays of compact size. Our method of construction also provides for a maximum radiating surface Without the necessity for accessory matching por tions, stubs, or transmission lines, all contributing to compact assembly.

For efficient use on aircraft any antenna must be light, compact, and present the smallest pos sible surface to reduce wind resistance, yet it must be large enough to ensure good pick-up and stability in operation. On an aircraft it is most desirable to have the shortest transmission leads possible, and a minimum of supporting structure for the antenna.

In a direction finding antenna array the dimensions of the entire array are dependent upon the restrictive dimensions of the individual radiating members; thus, the smaller the sizeof the individual radiating member, the more compact the entire system or array will become. However, as the size diminishes, the utility decreases due to diliiculties encountered in impedance matching and operation over a sufficiently wide range of frequencies. In accordance with our invention we provide an antenna of a type in which it is possible to obtain impedance matching over a relatively wide frequency band in consideration of the size of the antenna used, and having good performance at low radiation angles.

An important object of our invention is to provide an antenna of small size suitable for use on aircraft and small mobile vehicles.

A further object of our invention is to provide a self-supporting antenna so constructed as to incorporate features of compactness and strength,

as well as small cross-sectional area so as to reduce wind resistance to a minimum when mount ed in an air stream.

Another object of our invention is to provide an antenna suitable for use on high frequencies and ultra-high frequencies, having stable characteristics, and so designed as to obtain impedance matching over a relatively wide frequency band.

A better understanding of our invention and the objects and features of the invention may be 13 Claims.

larneter of conductor I.

had bywreference to the accompanying drawings wherein:

Fig. 1 is a vertical view in cross section of the antenna;

Fig. 2 is a cross-sectional view taken on line 2 2 of Fig. 1.

As shown in Fig. l, a length of tubular conductor I of a coaxial line section is rigidly mounted .in insulating ring 2, held in place on supe porting plate 3 by means such as bolt 4. Passing through the length of the tubular conductor I, and insulated from it by insulating spacers B and l, is a longer tubular conductor 8, extending well beyond the upper end of tubular conductor I. Tubular conductor 8 is preferably substantially twice the length of conductor I and of a diameter smaller than the inside di- It is now clear that conductor 8 has been inserted into conductor I to a depth equivalent to one-half the length of conductor 8, with the remaining half of conductor li extending upwardly beyond the end of conductor I. Passing through tubular conductor 8, and in turn insulated from it by spacers 9 and I0, is a center conductor II of the coaxial line section, extending the length of tubular conductor I. In other words, tubular conductor I and the center conductor II form the two conducting portions of a coaxial line section.

At a midpoint in the length of tube 8 a small aperture I2 is situated, for the passage of resistor I3, connecting inner conductor II and outer conductor I. Inserted in the said aperture I2 is a small insulating bushing I 4 surrounding resistor I3 as it passes through the aperture, and also providing a weatherproof closure. At the uppermost end of tube 8 is fastened a small weatherproong cap I5.

The exposed surfaces of the extended portion of conductor 8 and of the conductor I form the radiating members of the antenna. At the base of the antennaa lead I6 is fastened to center conductor II, for connection to one of the two conductors in dual cable I1. Likewise, lead I8 is fastened to outer conductor I for connection tothe other conducto-r of dual cable I l.

"Fig 2 shows the base of the antenna proper,

.with four bolts 4 held to supporting plate 3 by nect shield I9 of dual cable I'I to `a suitable ground' in known manner. v

With the diameter-to-length ratio considered in theconstructioma comparatively Wide frequency range may be covered if correct impedance matching is performed. Also, increasing the capacity-inductance ratio reduces the characteristic impedance, while the radiation resistance remains approximately a steady value. Since the combined radiation resistance of radiating member I `an'cl radiating member 8 vplus the actual resistance I3 give a total .resistive load, all that remains is to choose values for resistor I3 and proper lengths of the radiating members I and 8 in order to secure the impedance matching desired.

As will be seen from the fact that vconductor 8 lies partially in the eld of conducto-rs i 'and H, radiation energy is transferred between con ductor 8 and the conductors I, II. Also While thus transferring radiation energy conductors I and I I act also as a transmission line terminated in resistance I3. Upon adjustment of the vtotal resistive load to match the line impedance, there are no reflections -or standing waves, fand radiation occurs only on the external surfaces of conductor-radiator yI and radiator 8.

It is known that properly designed and constructed wideband antenna-s possess the characteristic of a nearly constant input impedance over a range of several rnegacycles. Since our invention and design allows for connection 4of the transmission line at the center of the radiator section where the impedance is 'at a minimum (and substantially equal to the radiation resistance), we have been able to obtain proper impedance matching vover a relatively wide frequency band, It follows that the actual length of each radiating member is dependent upon the above-mentioned variable factors. For very high frequency work, these lengths each approximate one-quarter the wave length of the particular value used (or 90 electrical degrees). At still higher frequencies, dimensions decreased relatively toward oneeighth wavelength ('or 45 electrical degrees).

While we have `described one 'specific structure 'by way of illustration many variations .in the details thereof may be had without departing from the scope of our invention. For instance, yit has been found that tubular conductors of circular cross-section are preferably 'at high vfrequencies to tubular conductors of other 'crosssectional design. The specific description shown here is given by way of example, and is not intended as a limitation of our invention as set forth in the objects thereof vand in the accompanying claims.

W'e claim:

l. An antenna having two .radiating .elements the dimensions of which are suitably vchosen for relatively wide frequency band operation, one only .of -said elements having connections 4to a transmission line of ygiven impedance, the other of said elements being substantially twice the length of said one element and having the lower half of its length surrounded by the same, the upper half of said other element being aradiating portion, a conductor kextending coaxially within said other element :and included in one of said connections, and a resistor extending through an orifice intermediate the ends of said other element and connected in series between said conductor and the adjacent end of said :one element, lthergeneral arrangement beingsuch'that energy transfer is obtained between the two said elements and an A.impedance match .is provided between said antenna and said transmission eline.

2. A dipole antenna the radiating members of which are suitably dimensioned for operating over a predetermined wave band, one of said members being constituted as a hollow conductor of a length substantially one-quarter wavelength at the midfrequency of said wave band, and 'of a givenv diameter, a linear conductor substantially coaxial to said hollow conductor and extending throughout the length thereof, impedance means interconnecting electrically one end of said hollow conductor and one end of said linear conductor, the other one of said radiating members being constituted as a second hollow conductor of a diameter less than that of the rst named conductor coaxial of and surrounding said linear conductor, extending throughout rthe length of said first named hollow conductor and beyond the end thereof in the :direction of said impedance means, the two said hollow conductors being suitably interrelated for 'mu-tual exchange of high frequency energy.

3. An antenna comprising rst and second vertical tubular conductors, said rst conductor being of predetermined length with relation to the midband frequency .at which operation is desired, with said first conductor being substantially equal to one-half the length of said second conductor, said second tubular conductor being insulatedly inserted coaxially into the bore -of said first tubular conductor, the' extent of insertion being equivalent t0 the length of said first conductor, a third linear conductor extending vertically coaxially through the bore of said second tubular conductor and being insulated therefrom, the length of said third linear conductor being substantially equal to the length of said first tubular conductor and disposed within the same, and means providing a resistive Aconnection from the uppermost end of said rst conductor to the uppermost termination of said third linear conductor.

4. An antenna comprising first and second vertical tubular conductors, said rst conductor being substantially a quarter Wavelength with relation to the midband frequency at which operation is desired, with said rst conductor being lsubstantially equal to one-half the length of Ysaid second conductor, said second tubular conductor being insulatedly vinserted coaxially into `the bore of said rst tubular conductor, the extent of insertion being equivalent to the length of rsaid rst conductor, a third linear conductor `extending vertically coaxially through the bore yrof said second tubular conductor and being insulated therefrom, the length of said 'third linear conductor being substantially equal to the length `of 'said first tubular conductor `and means for providing resistive connection from the uppermost end of said first conductor to the uppermost termination of said third linear conductor.

5. A dipole antenna comprising two hollow conductors of suitable dimensions to eectively radiate 'energy of a given frequency, the rst of said conductors being substantially twice the length of the second and having an outside diameter such as to permit insertion within the second conductor while being insulated therefrom, a supporting base common to the two conductors, a linear conductor substantially coaxial to said hollow vconductors and extending from said base to the height of said second conductor, impedanceimeans extending through a hole in saii'd 'first conductor and electrically interconnecting second conductor, and twin-conductor transmission line terminals connected respectively to the lower ends of said second conductor and said coaxial linear conductor.

6. An antenna for radiation and/or collection of radiant energy, said antenna comprising two hollow conductive tubular members, the rst having twice the length of the second and being so telescoped within the second that'the rst and second terminate in a common transverse plane, means providing electrical insulation between said members, a conductor extending from said transverse plane coaxially with respect Vto said members and within the same and reaching to a plane where the first member emerges from the second, said first member being oriced in that plane, and a resistor extending through the orice and connecting said conductor to said second member.

7. An up standing antenna for radiation and/or collection of radiant energy, comprising two tubular conductors and a solid conductor all coaxially rising from a common base and insulated one from the other, the outer tubular conductor and the solid conductor both terminating in a transverse plane which bisects the inner tubular conductor, connections to a transmission line from the lower extremities of said outer tubular conductor and said solid conductor respectively, and a resistor extending through an orice in said inner conductor at said bisecting plane, said resistor providing a connection between said outer conductor and said solid conductor.

8. An antenna having the radiating characteristics of a vertical dipole and comprising two tubular conductors which are coaxially erected from a common base, the inner conductor being of twice the height of the outer conductor, means for insulating said conductors one from the other, a resistor having one of its terminals connected to the upper end of said outer conductor and having the other of its terminals extending into the interior of said inner conductor in which an oriflee is provided therefor, and twin-conductor transmission line connections, one to the base of said outer conductor and the other through a coaxially disposed solid conductor to said other resistor terminal, said tubular conductors being electrically inter-coupled, whereby energy transfer is obtained therebetween.

9. An antenna according to claim 8, wherein the radiating surfaces of said tubular conductors are suitably dimensioned for eflicient operation at the mid-frequency of a desired Wave band.

10. An antenna according to claim 8 and further characterized in that the impedance of the tubular conductors is matched to that of the transmission line to which one of them is connected.

11. A dipole antenna the two arms of which are constituted as tubular conductors the first of which is telescoped within the second and is of twice the length of the second, the electrical center of said dipole being at the transverse plane where the first conductor emerges from the second, means including a solid conductor extending coaxially of the antenna for setting up an electrical field within the second conductor, thereby to cause radiation energy transfer to or from said first conductor, an impedance situated in said transverse plane and conductively interconnecting adjacent ends of the first conductor and said solid conductor, and a twin-conductor transmission line having impedance characteristics which match those of said antenna, one lead in said line being connected to said second conductor and the other lead being connected to .said solid conductor.

REFERENCES CITED The following references are of record in the nie of this patenti UNITED STATES PATENTS 

